【作者】 王博；

【导师】 李志远；

【作者基本信息】 华南理工大学 ， 物理电子学， 2020， 博士

【摘要】 光与微纳结构的相互作用一直是国际科学界很受青睐的一个研究热点,可为发展全光网络、量子信息等新兴技术提供重要的理论基础。然而,光与微纳结构的相互作用会涉及到许多复杂的物理过程,且往往比表面看起来要复杂得多,“狡猾”的多。因此,在研究纳米、亚纳米、乃至原子尺度上的光和物质相互作用时,需要人们审慎地看待这些问题。一般来说,光与微纳结构的相互作用可以有光学相互作用和量子相互作用。其中,量子相互作用涉及到微观层面的能级劈裂,反映了光与微观粒子间的相互作用在内能态上的变化,而光学相互作用涉及到宏观层面上的光学模式单元间的相干干涉和耦合,反映了光与宏观物质间的相互作用在外在表征上的物理变化。基于光子晶体学,表面等离激元光学,腔量子电动力学,量子光学以及腔光机械系统领域和平台,本论文对这些复杂体系里所涉及的光学相互作用和量子相互作用做了详细的分析,探求其中蕴含的新物理和新现象,并取得了一些研究成果。在多模微腔中,我们建立了基于时间调制的耦合模理论,实现了两个模式之间的光子跃迁。我们构建了光子晶体多模微腔,实现了基于光子跃迁的低Q值微腔模式和高Q值微腔模式之间的完全能量转换,继而设计了新型的动态光学存储器。此存储器可以有效地实现对信号光脉冲的捕获、超长时间的存储和快速释放的过程。另外,我们还发现光子寿命和操作带宽的基础关联限制可以被打破,使得延迟带宽积的值达到76。这种动态光学存储器在光子电路、全光信息处理和光通信领域有着广阔的应用前景。近年来,等离激元纳米腔和分子组成的强耦合系统获得广泛的关注,也存在着一些争议问题,即实验者观察到的光谱劈裂(散射谱等)是否可以与量子辐射体内的本征能级劈裂画上等号,从而能真实地反映量子辐射体的能态演化及劈裂现象。在本论文中,我们发现散射光谱对周围物质非常敏感,而巨大的光谱劈裂既源于单分子与等离激元的量子相互作用(量子拉比劈裂),也源于多分子与等离激元的经典光学相互作用。我们建立了一个能够定量区分光学和量子相互作用的物理模型和解析理论,其中利用洛伦兹模型来近似地描述分子和等离激元。我们发现相比于单分子拉比劈裂的量子相互作用,分子集体与纳米间隙等离激元的光学相互作用,是产生巨大光谱劈裂的主要原因。该理论还指出光学相互作用所引起的光谱劈裂量与√(N为分子数)同样成正比。简单地说,实验中所观察到的巨光谱劈裂并不是纯量子拉比劈裂,而是由所有分子集体与等离激元的光学相互作用产生的巨大频谱调制和单分子与等离激元强耦合的量子拉比劈裂所引起的较小光谱调制效应的协同作用之总和。基于上述相似的耦合系统,我们通过在金属纳米间隙内放置点光源来考察近场激发对分子-等离激元强耦合效应的影响。此激发模式不仅激发了表面等离激元还激发了光源附近的近场,而这两个场将相干叠加,成为金属纳米结构的总局域场。进一步发现,此总局域场可以压缩微腔的有效模体积。对于由金属纳米微腔和分子组成的强耦合系统,分子不仅仅可以与表面等离激元发生量子相互作用,还与近场发生量子相互作用。因此,我们在荧光光谱上发现拉比劈裂明显增大,拉比振荡的可逆相互作用明显增强。同时,我们还与已报道的实验结果做对比,发现近场激发模式下的耦合强度是远场激发模式的1.7倍。这项工作可以促进纳米尺度上新颖量子现象的研究以及相关应用的研发,例如芯片集成的量子信息处理、量子逻辑门和量子纠缠。最后,我们将研究领域拓展到腔光机械系统,探讨了原子-光子-机械振子的量子相互作用情况。我们提出了一个将描述原子与光子之间量子相互作用的全量子方法与描述机械振子的经典方法相结合起来的理论模型,并构造了一个时间依赖的哈密顿量。通过缀饰态的方法求解这个方程,我们发现系统的真空拉比劈裂是时间依赖的,即原子能级劈裂一直受到机械振子的调制。我们发现,即使原子与光场不共振,经典的能级反交叉(频域能级反交叉)依然可以出现,其原因是由于机械振子的相位调制在某一时刻补偿了原子-光子的失谐量。我们将此理论模型推广到极大振幅区域,发现机械振子的失谐补偿能力可以达到GHz水平。最后,我们的研究表明当原子和光子共振时,原子-光子-机械振子系统可以达到最大耦合强度。这些结果有助于开辟一条利用机械振子干涉和操纵光机量子平台中光与物质相互作用的新途径。总的来说,我们研究了在不同体系上所涉及的量子和光学相互作用。在多模微腔中,我们建立了基于时间调制的耦合模理论,实现了两个模式之间的光子跃迁。此光学相互作用机制为设计新型全光信息处理器件带来一定的理论指导意义。接着,在分子和等离激元耦合系统中,我们发现相比于单分子拉比劈裂的量子相互作用,分子集体与纳米间隙等离激元的光学相互作用,是产生巨大光谱劈裂的主要原因。该理论有助于理清微观分子在单光子光场驱动下的内在能级劈裂的真实大小,回答真实的量子拉比劈裂能达到多大数量级的问题,更重要的是,回答人类能够在多大程度上改变微观世界这一根本的科学问题。为了增强量子辐射体和金属纳米腔的量子相互作用,我们发现近场激发模式可以为量子辐射体提供两个相互作用通道:表面等离激元场和近场。这一发现有助于我们探索更多一腔多场的效应来增强量子相互作用强度,促进纳米尺度上新颖量子现象的研究。最后,我们研究了原子-光子-机械振子的量子相互作用系统,发现在机械振子的调制下,系统处于动态的能级劈裂状态,出现了时域的能级反交叉。这些结果有助于我们利用机械振子对量子相互作用系统进行干涉和调控,同时这一调控行为有机会在基础科学和高技术领域挖掘到新的应用。更多还原

【Abstract】 The interaction between light and nanostructure has been a greatly popular research field in the world,which provides an important theoretical basis for the development of all-optical networks,quantum information and other emerging technologies.However,the interaction between light and nanostructure involves many complex physical processes,which are much more complex than the surface.Therefore,when we study the interaction between light and matter on the nanometer,sub-nanometer and even atomic scale,we need to treat these problems carefully.Generally speaking,the interaction between light and nanostructure can be classified optical interaction and quantum interaction.Quantum interaction involves energy level splitting at the micro-level,reflecting the change of internal energy state,while the optical interaction involves the coherent interference and coupling between the optical mode elements on the macro-level,which externally reflects the physical changes.Based on the fields and platforms of photonic crystals,surface plasmon,cavity quantum electrodynamics,quantum optics and cavity optomechanical system,this paper has made a careful analysis and understanding of the optical interaction and quantum interaction for the complex systems.In the multimode microcavity,we established the coupled mode theory based on time modulation,and realized the photonic transitions between the two modes.In multimode microcavity of photonic crystals,we have realized the complete energy conversion between a low-Q value microcavity mode and an ultrahigh-Q value microcavity mode based on the photonic transitions,and then developed a new type of dynamic optical memory.This memory can effectively realize the process of capturing signal optical pulse,storing with ultralong time and fast releasing.In addition,we also found that the fundamental link between photon lifetime and operation bandwidth is broken,and a delay-bandwidth product of ～76 is achieved.This approach may pay the way for dynamical control of on-chip all-optical information processing and optical communication.In recent years,there is a controversial problem in the coupling system composed of plasmon cavity and molecules,that is,whether the spectral splitting(scattering spectrum,etc.)is equivalent to the intrinsic energy level splitting of quantum emitter,and truly reflect the energy state evolution and splitting phenomenon of the quantum emitter.In this work,we show that the scattering spectra are very sensitive to the surrounding matter,and the giant spectral splitting stems both from the quantum interaction of a single molecule with plasmons(Rabi splitting)and from the classical optical interaction of multiple molecules with plasmons.To be more quantitative,we use the Lorentz model to approximately describe molecules and plasmons.We found that the collective optical interaction is dominant to generate the giant splitting(in scattering spectra),which is also proportional to √(N is the number of molecule),over the quantum interaction of single-molecule Rabi splitting.Therefore,the observed giant spectral splitting is not a pure quantum Rabi splitting effect,but rather a mixture contribution from the large spectral modulation by the collective optical interaction of all molecules with plasmons and the modest quantum Rabi splitting of single-molecule strongly coupled with plasmons.Then,based on the above similar coupling system,by placing a point source in the metallic nanogap,i.e.near-field excitation,this excitation mode not only excites the surface plasmon but also excites the near-field near the point source,and these two fields will be a localized field of the metallic nanostructure.It is further found that the localized field can compress the effective mode volume of the microcavity.For the strong coupling system composed of metallic nanocavity and molecule,the molecule can not only interact with the surface plasmons,but also with the near-field.Therefore,we found that both the Rabi splitting in the fluorescence spectrum and the reversible interaction of Rabi oscillations have been enhanced obviously.Furthermore,we found that the coupling strength under the near-field excitation mode is 1.7 times of that under the far-field excitation mode.Therefore,this work can promote the research and development of many quantum technologies and related applications,such as on-chip quantum information processing,quantum logic gates and quantum entanglement.Finally,we extend our research to cavity optomechanical system,and build the quantum interaction system of atom-photon-oscillator.We propose a theoretical model that combines the full quantum method to describe the quantum interaction between atom and photon with the classical method to describe mechanical oscillators,and construct a time-dependent Hamiltonian.With the dressed state approach,we find that the Vacuum Rabi splitting of the system is time-dependent,that is,the splitting of the atomic energy level is always modulated by the mechanical oscillator.We show that even though the atom is not in resonance with photon,it is available to make a phase compensation by mechanical oscillator for the detuning,so that the avoided crossing in the frequency domain can also happen.We extend the theoretical model to the extremely-large-amplitude regime and find that the compensation can readily reach the GHz scale.Finally,our studies show that when the atom is in resonance with the photon,the coupling of the atom-photon-oscillator triple system can reach maximum strength.These results can help to open up a new avenue to explore and harness mechanical oscillators to interfere and manipulate light-matter interaction in optomechanical platform.In general,we have studied the quantum and optical interactions in different systems.In the multi-mode microcavity,we establish the coupled mode theory based on time modulation,and realize the photonic transitions between the two modes.This mechanism of optical interaction has some theoretical significance for the design of new all-optical information processor.Then,in the coupling system of molecules and plasmon,we find that compared with the quantum interaction of single molecule Rabi splitting,the collective optical interaction of molecules and plasmon is the main reason for the giant spectral splitting.This theory can help to figure out the true quantity of the intrinsic energy level splitting of microscopic molecule,answer the question of how large the true Rabi splitting can be,and more importantly find out the true power of human being and the limitation to change the microscopic world.In order to enhance the quantum interaction between the quantum emitter and the metallic nanostructure,we found that the near-field excitation mode can provide two interaction channels for the quantum emitter: the surface plasmon field and the near-field.This discovery will help us to study one cavity with multi-field effects to enhance the quantum interaction and promote the research of novel quantum phenomena on the nanoscale.Finally,we study atom-photonoscillator couplied system.We find that the system is in a state of dynamic energy level splitting under the modulation of mechanical oscillator,and the energy level anticrossing occurs in the time domain.These results are helpful for us to use the mechanical oscillator to interfere the quantum interaction system.At the same time,this modulation can possiblely find new applications in the field of basic science and high technology.更多还原